Microstructure development in laser-processed Al-Ti-Ni alloys with 25 at. % Ti

摘要

The microstructure of laser-processed (Al1-xNix)(3) Ti with Ni content ranging from 5 to 15 at. % has been studied by scanning-and transmission-electron microscopy (SEM and TEM). All samples contain Al-rich dendrites with Ni-rich interdendritic phases. The dendrites in the 5 at. % Ni alloy consist of the Al3Ti phase with the DO22 type structure, whereas the alloys containing 8 to 15 at. % Ni consist of the Al-67 Ni8Ti25 phase with the L1(2)-type structure. The lattice parameter of the L1(2) type structure of Al67Ni8Ti25 was determined by comparing the Higher Order Laue Zone (HOLZ) line patterns in experimental and calculated convergent beam electron diffraction disks. The lattice parameter was found to be a = 0.3935 +/- 0.0003 nm. Within the L1(2) type regions of the alloy with 8 at. % Ni, precipitates with a new primitive tetragonal structure was found. The cell dimensions are a = 0.39 nm and c = 1.18 nm. AINTi(2) with Ti:AI ratio equal to 2.0 +/- 0.2 was found as needles in interdendritic regions. The cell dimensions are consistent with a = 0.299 nm and c=1.361 nm and space group P6(3)/mmc. (C) 1998 Kluwer Academic Publishers. [References: 57]